Lactic acid (2-hydroxypropionic acid) has been increasingly used worldwide in the production of several biodegradable polymers motivated by modern applications in the medical field (as, for example, in artificial prosthesis) and in the pharmaceutical area (as, for example, in medicines with controlled release) and by the strong ecological appeal of using biodegradable polymeric materials based on lactic acid (polylactic acid) from plant substrates in place of plastic of mineral origin. The success of the employment of a green route for the production of polylactic acid requires a complex process that ensures the removal of all of the contaminants in a natural raw material, the isolation of lactic acid and the concentration of the same.
Below are listed the main processes presented in the prior art for the solution of problems of regeneration, purification and concentration of lactic acid produced in fermentation media. As the techniques differ significantly depending on the approach adopted in each invention, subsections are adopted depending on the technology used as base of each patent document.
Generally speaking, it is verified that all of these technologies have as focus the isolated solution of problems of regeneration, purification or concentration which, separately, are ineffective in producing high-purity lactic acid from fermentative liquor with fibers, shells and other hardly removable impurities.
Processes of Membrane Permeation
U.S. Pat. No. 4,110,175 patent document refers to a electrodialysis process that uses anionic and cationic membranes with the purpose of removing organic acids including lactic acid, present in fruit juices and other aqueous solutions.
EP 230021 patent document describes a continuous fermentative process coupled to a electrodialysis process for the continuous removal of lactic acid. However, as there are separations and preliminary filtrations, various components of the fermentative liquor are adhered to the surface of polymeric membranes, which implies in a significant increase in the consumption of electrical energy.
Boyaval et al. (Biotechnology Letters, vol. 9, n° 5, pp. 207-212, 1987) presented a process composed of three unit operations: lactate production via fermentation, removal of cells and cell fragments through ultrafiltration and concentration/purification of lactic acid by electrodialysis. However, as prefiltration are not made, ultrafiltration membranes permeability is reduced drastically over time, requiring frequent chemical cleaning of ultrafiltration modules.
U.S. Pat. No. 5,002,881 patent document refers to a fermentation process in which the fermentation product undergoes an operation of ultrafiltration where the retained returns to the fermentation dorna and the permeate corresponding to a solution of ammonium lactate is concentrated through a reverse osmosis operation. Concentrated ammonium lactate is then fed to the electrodialysis operation for recovery and purification of lactic acid. During electrodialysis ammonia hydroxide is formed, which can be returned to the fermentation for pH correction. As disadvantage it can be highlighted the fact that the solution of concentrated ammonium lactate has also unconverted sugars, vitamins, proteins and other contaminants, thus contributing to the electrodialysis efficiency decrease and resulting in a thermally unstable product.
U.S. Pat. No. 5,503,750 patent document refers to a process with a membrane separation operation sequence (ultrafiltration, nanofiltration and reverse osmosis) for the concentration of an ammonium lactate solution and subsequent conversion into lactic acid. As a disadvantage of this process one can highlight the low recovery efficiency (of approximately 54%), other than the fact that the conversion of ammonium lactate into lactic acid uses ion exchange resins (which implies in a large amount of resins, and require subsequent regeneration operations).
U.S. Pat. No. 4,882,277 patent document aims to simplify all the steps used for the purification of lactic acid using only three unit operations: microfiltration, ultrafiltration, and electrodialysis, performed continually throughout the fermentation. The focus of this document is in the arrangement of conventional electrodialysis operation on a laboratory scale.
Complementing the previous document, the U.S. Pat. No. 4,885,247 patent document proposes an arrangement closer to the industrial application, highlighting the possibility of return of residual lactate to the fermenter in order to decrease the alkaline solution demand for controlling the acidity of the medium and reduce process losses.
U.S. Pat. No. 6,319,382 patent document refers to a fermentation (using ammonia to pH correction), purification and regeneration process of lactic acid that consists of a fermentation step, followed by microfiltration and ultrafiltration for withdrawal of cells, cell fragments and macromolecules. The permeate passes through ion exchange resins (chelate resin) for the substitution of bivalent cations by monovalent cations (such as sodium), thus avoiding the formation of insoluble salts that could damage the membranes of the subsequent electrodialysis process. The permeated having no bivalent cations then is submitted to an electrodialysis process for the regeneration of conventional acid and then to the bipolar electrodialysis to acid concentration. One may highlight as a disadvantage of this process the fact of having a high consumption of chemicals for the regeneration of ion-exchange columns, the product loss corresponding to the hold-up (retention) of ion exchange columns in each regeneration, and the requirement for a proper monitoring of the contamination of regenerative solutions. Moreover, these operations do not guarantee the withdrawal of organic contaminants that generate color to the product and lead to thermal instability by the formation of Maillard compounds.
US 2004/033573 A1 American patent document refers to a process that uses membrane separation steps including ultrafiltration, nanofiltration, reverse osmosis and electrodialysis. In this proposal, the fermentative liquor is ultraconcentrated for the retention of high molecular weight substances. Acidification of the permeated is then made to a pH below 3.9. The acidified solution undergoes a step of isolation via nanofiltration and/or reverse osmosis, which promotes the retention of bivalent ions, proteins, other nutrients and organic anions (such as the lactate anion) and permeates molecules free of charge (such as sodium lactate). Afterwards, it may be considered the use of bipolar electrodialysis for the concentration of the lactic acid solution. The use of nanofiltration and/or reverse osmosis constitutes an alternative to conventional electrodialysis process.
Ion Exchange Processes
EP 0393818 European patent document complements the U.S. Pat. No. 4,885,247 American patent document, including two steps of ion exchange after the electrodialysis step. Strong acidic ion exchange resins are used for the removal of sodium cations that were not removed during conventional electrodialysis and basic ion exchange resins weak to remove sulfate anions.
U.S. Pat. No. 5,571,657 patent document proposes modification of strong acidic ion exchange resins through contact with ammonium and/or amine solutions, so as to increase their selectivity to the Na+ cation, thereby increasing the efficiency of the lactic acid regeneration process of sodium lactate solutions.
Extractive Processes
U.S. Pat. No. 4,275,234 patent document presents a recovery process of organic acids aqueous solution using an initial organic solvent extraction followed by a second heated water extraction. It is worth noting that this application is restricted to solutions wherein the organic acid is in its free form.
BR8906651 Brazilian patent document proposes a process for purification and recovery of lactic acid from the solutions containing the same, through a sequence of liquid-liquid extractions. Initially, an aqueous solution of lactate and lactic acid is added with a complex forming agent (composed of at least one octol macolytic) generating octol-lactic acid. Afterwards, this aqueous phase passes through a liquid-liquid extraction with an organic solution of saturated halogenated cyclo-alkanes, alkylated and/or halogenated aromatic hydrocarbons and petroleum ether. The organic phase is separated and then passes through a liquid-liquid extraction with water or methanol. As disadvantages, one can highlight the high reaction time for the complex formation (about 8 h), the need of expensive complexing agents and risks associated with the use of aromatic organic solvents that imply a series of operational difficulties.
Works such as those of B. Bar and J. L. Geiner (Biotechnology Progress, vol. 3, n. 109, 1987), Malmary et al (J. Chem. Technol. Biotechnol., n. 75, pp. 1169-1173, 2000), Hartl and Marr (Separation Science and Technology, n. 28, pp. 805-819, 1993) and San-Marín and Cheryan (J. Chem. Technol. Biotechnol., n. 65, pp. 281-285, 1996) attested the separation efficiency of lactic acid extraction in an aqueous solution by means of long-stream trialkylamines and low basicity, which are able to form complexes with carboxylic acids for even low concentrations of solute, keeping a high selectivity.
U.S. Pat. No. 4,444,881 patent document presents a process capable of purifying organic acids of a diluted solution from fermentation. This solution is treated with a tertiary amine carbonate (for example, tributylamine or tricyclohexylmethylamine), resulting in a precipitate of calcium carbonate and organic salt of trialkylammonium. Organic salt solution is isolated, concentrated by extraction with solvent, distilled and heated for the generation of lactic acid and tertiary amine. As a disadvantage it may be highlighted the cost of specific chemical products, such as tertiary amines, and the absence of organic acids post-treatments to ensure the absence of impurities.
U.S. Pat. No. 4,771,001 patent document presents a process for continuous removal of lactate during fermentative liquor of cheese whey. During fermentation the separation and recycling of cells is made via microfiltration and ultrafiltration, wherein the permeate follows the purification steps. The permeate is acidified and then passes through a liquid-liquid extraction with a solution (immiscible in water) of a tertiary trialkylamine of 24 carbons, and an organic solvent. The organic phase is then separated and passes through a liquid-liquid extraction using a suspension of alkali solids and alkali-earth solids in an aqueous solution of ammonium hydroxide, which promote the removal of lactate and lactic acid. In this patent document concentration steps are not addressed or even lactic acid isolation.
U.S. Pat. No. 5,510,526 patent document uses as extracting phase a trialkylamine solution with a strong attraction to lactic acid (for example, tri-n-octylamine and tri-n-dodecylamine) in an extraction with atmosphere of CO2. Sodium bicarbonate crystals are formed and separated from the aqueous phase. Bicarbonate is converted to carbonate and returns to the fermentation process being used for pH neutralization. The alkylamine type used should be chosen so that its power of attraction is high enough to extract the lactic acid from lactate solution and weak enough to deliver the acid to the water. Because they are viscous, these alkylamines should be added from kerosene and/or octanol. The removal of lactic acid from the organic phase is done through contact with water. In the case of kerosene or octanol being used, a step prior to rinsing with water must be made to remove these solvents.
U.S. Pat. No. 6,478,965 patent document presents a route in the use of secondary or tertiary amines (e.g., TEA, or DEMA) in the extraction of water from a stream diluted in lactic acid (about 3%), thus producing a concentrated stream of 15% lactic acid. It is necessary a series of contactors to promote the extraction of water from the organic phase.
U.S. Pat. No. 6,509,179 patent document combines a set of unit operations for purification of lactic acid formed by the steps of acidification, salt removal, activated carbon filtration, primary extraction, secondary extraction, evaporation and vacuum distillation.
U.S. Pat. No. 7,026,145 patent document proposes an improvement in the process of lactic acid extraction using tertiary alkylamines using sulfuric acid along with the amine solution, as well as a preliminary acidification step using this same acid.
US 2004/210088 A1 American document describes several routes of lactic acid production based on liquid-liquid extraction with amines and/or and specific alcohols, the removal of the solvent being made by distillation columns in the top product or in the bottom product (depending on the route considered).
U.S. Pat. No. 7,019,170 patent document describes the recovery of lactic acid from a lactic acid solution and lactate through a sequence of liquid-liquid extraction operations. A first liquid-liquid extraction column promotes the exchange of mass between a stream of lactic acid and lactate and a stream of trialkylamine, generating a stream of primary raffinate and a saturated trialkylamine stream. The saturated trialkylamine stream passes through a column of liquid-liquid extraction with pure water, generating a stream of pure lactic acid and a stream of trialkylamine “alive”. A third column of liquid-liquid extraction promotes contact between the primary and raffinate trialkylamine stream “alive”, generating a stream of secondary raffinate and a stream of trialkylamine recovered (which can be returned to the first extraction operation).
Evaporative Processes
U.S. Pat. No. 6,489,508 patent document details the process of lactic acid concentration by evaporation highlighting the optimum operating conditions of either pressure (vacuum) and temperature, so as to minimize the change of color of the final product.
The international publication WO 00/56693 A1 describes a vacuum distillation process followed by crystallization, which allows the concentration of a solution of 80% lactic acid up to a concentration of 99%. The high energetic consumption of the evaporation and crystallization operations coupling is a significant disadvantage of this proposal.
U.S. Pat. No. 6,384,276 patent document proposes the acidification of a lactic acid and sodium lactate solution. Then, an evaporative crystallization is made, wherein which sodium lactate is crystallized and the lactic acid is kept in solution. It is observed, however, that the success of this proposal depends on having as load a pure solution (free of sugars, proteins, or vitamins), otherwise there will be contamination of the final product and the generation of a product with color.
Alternative Processes
U.S. Pat. No. 5,177,008 patent document proposes the use of chromatographic separation operations for the separation of lactic acid for the reuse of that product from the secondary streams of the ethanol industry. However, the high cost of this process, mainly for production of lactic acid on a large scale, significantly restricts the application of this technology.
CN 101234960 patent document proposes a concentration process which promotes initial evaporation of lactic acid followed by rotating distilling (also called molecular distillation), generating a stream of lactic acid with high purity.
It would be helpful if the technique had a process of obtaining lactic acid from fermentation broths that use clarification, regeneration, purification and liquor concentration, the process operating under energetic efficiency regimen by recycling the process streams, the final product being concentrated lactic acid and having high purity degree.